Anti-apo-B-48 monoclonal antibody, hybridoma producing the same, and method for measuring apo-B-48 using the same

ABSTRACT

A novel monoclonal antibody which specifically binds to apo-B-48 is disclosed. The monoclonal antibody specifically binds to apo-B-48 but does not bind to apo-B-100.

BACKGROUND OF THE INVENTION

[0001] I. Field of the Invention

[0002] The present invention relates to a monoclonal antibody whichspecifically binds to apo-B-48, hybridoma producing the same and methodfor measuring apo-B-48 using the monoclonal antibody. The monoclonalantibody is useful for diagnosis and therapy of hyperlipidemia andarterial sclerosis.

[0003] II. Description of the Related Art

[0004] Arterial sclerosis is one of the typical adult diseases andestablishment of effective diagnosis and therapy of this disease islonged for. The causes of arterial sclerosis include increase in theamounts of various lipoproteins contained in the blood circulating thebody, which accelerate deposition of cholesterol on the inner walls ofblood vessels, and decrease in various lipoproteins which prevent suchdeposition of cholesterol.

[0005] Representative lipoproteins which are known to participate inhyperlipidemia include chylomicron (CM), chylomicron remnant (CMremnant) which is an intermediate metabolite of CM in the blood, verylow density lipoprotein (VLDL), very low density lipoprotein remnant(VLDL remnant) which is an intermediate metabolite of VLDL in the blood,low density lipoprotein (LDL) and high density lipoprotein (HDL).

[0006] CM remnant, VLDL remnant and the like are called remnant-likeparticles (RLP). The remnant-like particles as well as LDL arelipoproteins which transport cholesterol to the blood vessel walls.Therefore, to decrease the blood levels of these lipoproteins is adirect therapy of arterial sclerosis. On the other hand, since HDL, forexample, has a function to withdraw cholesterol from the lesion ofarterial sclerosis, to increase the blood level of HDL is useful for thetherapy of arterial sclerosis.

[0007] Among the above-mentioned lipoproteins, RLP has been reported toparticipate in expression of arterial sclerosis due to postprandialhyperlipidemia, and is now thought as an important risk factor ofarterial sclerosis. Known apolipoproteins constituting RLP includeapo-C, apo-E, apo-A-I, apo-B-100 and apo-B-48.

[0008] One of the known methods for measuring blood level of RLP is theRLP-C (remnant-like particles cholesterol) method. In the RLP-C method,anti-apo-A-I monoclonal antibody and anti-apo-B-100 monoclonal antibodyare immobilized on a gel, and the gel is reacted with a test sample,followed by removal of the lipoproteins bound to these antibodies bycentrifugation. Thereafter, the amount of the lipoprotein remaining inthe supernatant is measured in terms of the amount of cholesterol.

[0009] Apo-A-I occurs as a major apolipoprotein of CM and HDL, andapo-B-100 occurs as a major apolipoprotein of VLDL, VLDL remnant andLDL.

[0010] Thus, theoretically, CM and HDL are bound to the anti-apo-A-Imonoclonal antibody, and VLDL, VLDL remnant and LDL are bound toanti-apo-B-100 monoclonal antibody. Thus, in the RLP-C method, theselipoproteins are removed.

[0011] The anti-apo-B-100 monoclonal-antibody specifically recognizesthe region of the 2291st to 2318th amino acids, so that it does notrecognize apo-B-48 which consists of the 1st to 2152nd amino acids ofapo-B-100. Therefore, the lipoprotein which contains apo-B-48 as anapolipoprotein but does not contain apo-B-100 as an apolipoprotein ismeasured by the RLP-C method.

[0012] The structure of the epitopes on the apolipoproteins and thehomigenity of the epitopes in the plasma lipoprotein population stillremain unclear.

[0013] In the RLP-C method, the above-mentioned removal of the variouslipoproteins by binding the lipoproteins to the gel is indispensable.However, this step is troublesome and has poor reproducibility becausethe degree of removal varies from run to run. Therefore, the measuredvalues are not very reliable.

[0014] Apo-B-48 is contained as an apolipoprotein in CM and CM remnant.CM is quickly converted to CM remnant after eating by lipoprotein lipaseand the CM remnant is taken into the liver through remnant receptorsexisting in the liver, so that CM does not exist in the blood whenfasted. That is, Chylomicrons are lipoproteins synthesized exclusivelyby the intestine to transport dietary fat and fat-soluble vitamins.Among the apoliporoteins found in chylomicrons, such as apo-B-48,apo-A-I, apo-A-IV and Cs, only the synthesis of apo-B-48 is required forthe assembly of chylomicrons. Apo-B-48 is a 2152 amino acid longpolypeptide translated and pooled in the adult intestine from the samegene as apo-B-100 by the action of a series of enzymes. Duringcirculation in the blood, chylomicrons are exposed to lipolysis andapolipoprotein exchange, and are converted into “chylomicron remnants”.Therefore, if there is a monoclonal antibody which specificallyrecognizes apo-B-48, CM remnant alone can be directly measured by usingthe blood when fasted as a test sample as a risk marker for postprandiallipidemia and/or arterial sclerosis. This makes it possible toaccurately diagnose hyperlipidemia and, in turn, is useful for diagnosisand therapy of arterial sclerosis.

[0015] Apo-B-48 has the same amino acid sequence as a part of the aminoacid sequence of apo-B-100. The amino acid sequences of both apo-B-100and apo-B-48 are known (Nature, Vol. 323, p.738, October, 1986). Ananti-apo-B-48 antiserum is also known (Journal of Biological Chemistry,Vol. 265, No. 15, p.8358, 1990; Journal of Biological Chemistry, Vol.267, No. 2, p.1176, 1992; and Clinical Science, Vol. 85, p.521, 1993).

[0016] However, a monoclonal antibody which specifically binds toapo-B-48 alone has not been reported. Moreover, a reference (RINSHOKENSA, Vol. 40, No. 9 (1996), p.1025, left column, line 8 from thebottom) describes that it is theoretically difficult to produce anantibody which specifically reacts with apo-B-48 alone.

SUMMARY OF THE INVENTION

[0017] Accordingly, an object of the present invention is to provide amonoclonal antibody which specifically reacts with apo-B-48 alone.Another object of the present invention is to provide a hybridoma whichproduces the monoclonal antibody according to the present invention.Still another object of the present invention is to provide a method formeasuring apo-B-48 in a test sample using the monoclonal antibodyaccording to the present invention. Still another object of the presentinvention is to provide a reagent and a kit for immunoassay formeasuring apo-B-48 in a test sample.

[0018] The present inventors intensively studied to provide a monoclonalantibody which specifically reacts with apo-B-48 alone, to succeed inobtaining such a monoclonal antibody by using a conjugate of a verysmall peptide consisting of the C-terminal region of apo-B-48 and acarrier protein as an immunogen.

[0019] That is, the present invention provides a monoclonal antibodywhich specifically binds to apo-B-48 and which does not specificallybind to apo-B-100. The present invention also provides a hybridoma whichproduces the monoclonal antibody according to the present invention. Thepresent invention further provides a method for measuring apo-B-48 in atest sample, comprising utilizing antigen-antibody reaction betweenapo-B-48 in the test sample and the monoclonal antibody according to thepresent invention. The present invention still further provides areagent for immunoassay for measuring apo-B-48 comprising the monoclonalantibody according to the present invention. The present invention stillfurther provides a kit for immunoassay for measuring apo-B-48 comprisingthe monoclonal antibody according to the present invention.

[0020] By the present invention, a monoclonal antibody whichspecifically binds to apo-B-48 and which does not specifically bind toapo-B-100 was first provided. Since the monoclonal antibody according tothe present invention specifically binds to apo-B-48 but does notspecifically bind to apo-B-100, apo-B-48 alone can be measured. Thus,the monoclonal antibody of the present invention is useful for thediagnosis and therapy of arterial sclerosis.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 schematically shows the results of the Western blot showingthe reactions between monoclonal antibody B48-151 of the presentinvention and various lipoprotein fractions, which results were obtainedin Example 5;

[0022]FIG. 2 schematically shows the results of the Western blot showingthe reactions between monoclonal antibody B48-151 of the presentinvention and various lipoprotein fractions, when the reactions wereinhibited by peptide C6, which results were obtained in Example 5;

[0023]FIG. 3 shows the calibration curves obtained in ELISA utilizingimmobilized monoclonal antibody B48-151, obtained in Example 6;

[0024]FIG. 4 shows the results of the ELISA utilizing immobilizedmonoclonal antibody B48-151, which was carried out using sera fromhealthy individuals as samples, obtained in Example 7;

[0025]FIG. 5 shows the results of the ELISA utilizing immobilizedmonoclonal antibody B48-151, which was carried out in the presence orabsence of various surfactants, which results were obtained in Example8; and

[0026]FIG. 6 shows the results of the ELISA utilizing immobilizedpeptide C6, in the presence or absence of various surfactants, whichresults were obtained in Example 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] As mentioned above, the monoclonal antibody according to thepresent invention specifically binds to apo-B-48 and does notspecifically bind to apo-B-100. The corresponding epitope of themonoclonal antibody according to the present invention may preferablyreside in the C-terminal region of apo-B-48. The C-terminal region maypreferably be 1st to 20th, more preferably 1st to 10th amino acids fromthe C-terminal of apo-B-48. The corresponding epitope may preferablyinclude the C-terminal of apo-B-48. As will be described later indetail, the corresponding epitope of the preferred monoclonal antibodyactually produced in the examples is the peptide consisting of only 6amino acids of the C-terminal region of apo-B-48.

[0028] The monoclonal antibody according to the present invention may beobtained as follows:

[0029] First, a peptide derived from apo-B-48 is synthesized. Thepeptide may preferably consists essentially of 5 to 20 amino acids, morepreferably 5 to 10 amino acids from the C-terminal of apo-B-48(excluding cystein which may be attached to the N-terminal of thepeptide). For example, a peptide consisting of the 6 amino acids fromthe C-terminal of apo-B-48, to which cystein is attached at theN-terminal thereof, that is, a peptide consisting of 7 amino acidshaving the sequence of Cys Leu Gln Thr Tyr Met Ile (this peptide ishereinafter referred to as “C6”) is synthesized.

[0030] The peptide derived from apo-B-48, such as the above-mentionedC6, is then conjugated with a carrier protein such as hemocyanin. The C6may be bound to the carrier protein through the N-terminal cystein. Thismay be accomplished by the method described in detail in the Examplesbelow.

[0031] Using the thus obtained conjugate as the immunogen, themonoclonal antibody according to the present invention may be preparedby the well-known conventional method. An example of the method isdescribed in detail in the Examples below. Briefly, a mammal isimmunized with the conjugate and antibody-producing cells, such aslymphocytes and spleen cells are collected from the immunized mammal.The antibody-producing cells are then fused with myeloma cells, andhybridomas are selected by selective culture. The monoclonal antibodiesproduced by the obtained hybridomas are then tested for theirspecificities by Western blot (WB) method or by ELISA using apo-B-48 orapo-B-100 as an antigen, and the hybridomas producing monoclonalantibodies which bind to apo-B-48 and do not bind to apo-B-100 areselected, thereby obtaining the monoclonal antibody according to thepresent invention. As the antigen, not only the free apolipoproteins,but also lipoproteins containing the apolipoproteins may be employed.

[0032] By this method which is described in more detail in the Examplesbelow, a hybridoma named B48-151 producing the monoclonal antibodyaccording to the present invention was obtained. The hybridoma B48-151has been deposited with National Institute of Bioscience andHuman-Technology, Agency of Industrial Science and Technology at 1-3,Higashi 1-chome, Tsukuba-shi, Ibaraki 305-0046 Japan under accession No.FERM BP-6473.

[0033] The monoclonal antibody produced by the hybridoma B48-151 is apreferred monoclonal antibody according to the present invention, whichstrongly and specifically reacts with apo-B-48 and do not specificallyreact with apo-B-100 at all. Monoclonal antibodies produced by variantsof the hybridoma B48-151 are also preferred. The term “variant” hereinmeans the hybridomas derived from the hybridoma B48-151 having the sameor modified physiological and/or morphological characters as thehybridoma B48-151 and produces a monoclonal antibody which specificallybinds to apo-B-48 and which does not specifically bind to apo-B-100.

[0034] The monoclonal antibody according to the present invention may beused for measuring apo-B-48 in a test sample by immunoassay. Since notonly free apo-B-48, but also apo-B-48 contained in lipoproteins can bemeasured, the monoclonal antibody may be used for immunoassays formeasuring the lipoproteins containing apo-B-48.

[0035] In the present specification and claims, the term “measure”includes both quantification and detection.

[0036] The test sample may be a body fluid such as blood, serum or bloodplasma, as well as dilutions thereof, although the test sample is notrestricted thereto.

[0037] Various methods for immunoassay are well-known in the art and themonoclonal antibody according to the present invention may be applied toany of these methods. That is, known immunoassay methods include, whenclassified according to the reaction mode, sandwich methods,immunoblotting methods, competition methods, agglutination methods andso on. When classified according to the label used, known immunoassaysinclude enzyme immunoassays, radio immunoassays, fluorescenceimmunoassays, biotin immunoassays-and so on.

[0038] Among these, sandwich ELISA and Western blot are preferred. Thesemethods per se are well-known in the art, and detailed methods aredescribed in the Examples below.

[0039] Briefly, sandwich ELISA may be carried out, for example, asfollows. That is, the monoclonal antibody of the present invention isimmobilized on a solid carrier such as walls of wells in a microtiterplate or microbeads. After the immobilization, the solid carrier isblocked with proteins such as skim milk, casein, gelatin, bovine serumalbumin or the like to prevent nonspecific binding of the antigen. Atest sample is applied to the solid carrier and antigen-antibodyreaction is allowed to occur. After washing the carrier, anenzyme-labeled second antibody to apo-B-48 is applied andantigen-antibody reaction is allowed to occur. After washing, the secondantibody bound to the carrier is measured based on the color reactionafter adding a substrate of the enzyme.

[0040] Western blot method may be carried out, for example, as follows.That is, a test sample is subjected to fractionation by gelelectrophoresis such as SDS-PAGE, and the electrophoretic pattern istransferred onto a membrane such as nitrocellulose membrane. Afterblocking the membrane, the monoclonal antibody of the present inventionis applied to the membrane and antigen-antibody reaction is allowed tooccur. After washing, a labeled second antibody to the monoclonalantibody is applied and antigen-antibody reaction is allowed to occur.After washing, the second antibody bound to the membrane is measured bymeasuring the label.

[0041] In the method of the present invention, it is preferred tosubject the test sample to a treatment which exposes the epitope ofapo-B-48, which epitope is recognized by the monoclonal antibodyaccording to the present invention. That is, in cases where themonoclonal antibody according to the present invention recognizes theC-terminal region of apo-B-48, and where the test sample is a body fluidcontaining lipoprotein particles or a dilution thereof, theantigen-antibody reaction between apo-B-48 and the monoclonal antibodymay not occur very well because the C-terminal region of apo-B-48 maynot be well exposed in lipoprotein particles. Thus, in such a case, itis preferred to expose the C-terminal region of apo-B-48.

[0042] Exposing the C-terminal region of apo-B-48 may be accomplished bytreating the test sample with a surfactant, or by subjecting the testsample to freeze-thaw cycle at least once.

[0043] As the surfactant useful for exposing the C-terminal region ofapo-B-48, nonionic surfactants including polyoxyethylene-p-t-octylphenylethers such as Triton X-100 (trademark), Triton X-114 (trademark) andNonidet P40 (trademark); and polyoxyethylene sorbitane alkyl esters suchas Tween 20 (trademark). These surfactants may be employed individuallyor in combination. In cases where a Triton series surfactant such asTriton X-114 (trademark) which has high epitope-exposing ability but notdissolved well at room temperature is employed, it is preferred to use amixture of the Triton series surfactant and a Tween series surfactantsuch as Tween 20 (trademark) which is well dissolved at room temperatureand which does not substantially inhibit the antigen-antibody reactions.

[0044] Although use of SDS to expose an epitope of apo-B-48 has beenreported (Makoto KINOSHITA et al., Abstract of the 30th Meeting of JapanArterial Sclerosis Association held on Jun. 11 and 12, 1998, p.133), SDSis not preferred in the present invention because the antigen-antibodyreaction may be inhibited.

[0045] Since surfactants tend to inhibit immunological reactions, theconcentration of the surfactant may preferably be selected such that thesurfactant does not substantially inhibit the immunological reactions.The preferred concentration of the surfactants may preferably be 0.01 to2% by weight, more preferably 0.02 to 0.5% by weight. The treatment maypreferably be carried out at 4 to 40° C. for 5 minutes to 48 hours in abuffer used for the antibody-antigen reaction. The surfactant may existin the reaction mixture of the antigen-antibody reaction. Thus, thetreatment may be carried out simultaneously with the antigen-antibodyreaction, or before the antigen-antibody reaction.

[0046] The epitope of apo-B-48 may also be exposed with destroying thestructure of the lipoproteins by repeating freezing and thawing cycle ofthe test sample. The freeze-thaw cycle may be carried out at least once.

[0047] The present invention also provides a key reagent for immunoassayfor measuring apo-B-48. The reagent may be in the form of a solidcarrier on which the monoclonal antibody of the present invention isimmobilized. The monoclonal antibody may be immobilized on gelatinparticles or latex particles by a conventional method to prepare areagent for immunoassay by agglutination method. Similarly, themonoclonal antibody may be immobilized on a solid carrier such as wallsof wells of microtiter plate, polymers such as polystyrene, glass beads,magnetic particles, filter paper for immunochromatography, glass filteror the like by a conventional method to prepare reagent for enzymeimmunoassay (EIA), ELISA, radio immunoassay (RIA) or the like.

[0048] Further, the present invention also provide a kit for immunoassayfor measuring apo-B-48. The kit may comprise, in addition to theabove-mentioned reagent including the monoclonal antibody of the presentinvention bound to a solid carrier, at least one or more of a secondlabeled antibody, reagents for measuring the label of the secondantibody, blocking agent, buffer and the like.

EXAMPLES

[0049] The present invention will now be described by way of examplesthereof. The Examples are presented for the illustration purpose onlyand should not be interpreted in any restrictive way.

Example 1 Synthesis of Peptide Originated from Apo-B-48

[0050] A peptide consisting of the 4 amino acids from the C-terminal ofapo-B-48, to which cystein was attached at the N-terminal thereof, thatis, a peptide consisting of 5 amino acids having the sequence of Cys ThrTyr Met Ile (this peptide is hereinafter referred to as “C4”) wassynthesized by a commercially available peptide synthesizer.

[0051] Similarly, a peptide consisting of the 5 amino acids from theC-terminal of apo-B-48, to which cystein was attached at the N-terminalthereof, that is, a peptide consisting of 6 amino acids having thesequence of Cys Gln Thr Tyr Met Ile (this peptide is hereinafterreferred to as “C5”) was synthesized.

[0052] Similarly, a peptide consisting of the 6 amino acids from theC-terminal of apo-B-48, to which cystein was attached at the N-terminalthereof, that is, a peptide consisting of 7 amino acids having thesequence of Cys Leu Gln Thr Tyr Met Ile (this peptide is referred to as“C6” as mentioned above) was synthesized.

[0053] The synthesis of the peptides was carried out using an automaticpeptide synthesizer PSSM-8 commercially available from ShimazuCorporation, Kyoto, Japan, for simultaneous synthesis of a plurality ofspecies by solid method. All of the amino acids were L-amino acids. Theα-amino group was protected by 9-fluorenylmethoxycarbonyl group (Fmocgroup), the β-sulfhydryl group of cystein and γ-carboxamide group ofglutamine were protected by trityl group, and β-hydroxyl group ofthreonine and phenolic hydroxyl group of tyrosine were protected byt-butyl group.

[0054] As the solid carrier for initiating the peptide synthesis, 30 mgof HMP isoleucine resin (commercially available from Perkin Elmer) towhich isoleucine (the C-terminal of the peptides) had been preliminarilyattached in an amount of 0.65 mmol/g was used. For the condensation,2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluroniumhexafluorophosphate,1-hydroxybenzotriazole and N,N-diisopropylethylamine were used. For theremoval of Fmoc group, 30% piperidine/DMF (dimethylformamide) solventwas used. As the solvent for reaction, DMF was used. The three peptideswere simultaneously synthesized in accordance with the standard protocoldescribed in the instructions attached to PSSM-8.

[0055] After the synthesis, the carriers to which the peptidescontaining the protective groups were attached were washed withmethylene chloride and dried. The yields of C4, C5 and C6 were 41.0 mg,48.4 mg and 52.6 mg, respectively.

[0056] Each of the carriers to which the peptide was bound was treatedwith trifluoroacetic acid solution (1 ml of trifluoroacetic acid, 50 μlof water, 75 mg of phenol, 50 μl of thioanisole and 50 μl of ethanediol)for 2 hours at room temperature to obtain free peptide chain. Thepeptide was precipitated with diethyl ether, and the precipitate wasrecovered by filtration. The precipitate was dissolved in water andfreeze-dried. The yields of the thus obtained crude peptides C4, C5 andC6 were 12.23 mg, 16.17 mg and 17.04 mg, respectively.

[0057] The thus obtained crude peptides were purified by reverse phasehigh performance liquid chromatography. The column was Cosmosil5C18-AR-300 (20 mm I.D.×150 mm L, commercially available from NacalaiTesque) and elution was carried out with 18-28% linear gradient ofaqueous acetonitrile solution containing 0.1% trifluoroacetic acid. Theyields of the purified peptides C4, C5 and C6 after freeze-dry were 7.12mg, 11.75 mg and 10.71 mg, respectively. Aliquots of these peptides weresampled and their sequences were confirmed by a protein sequencer(Procise 494 commercially available from Perkin Elmer).

Example 2 Synthesis of Peptide-KLH Conjugates

[0058] In 400 μl of 0.1 M phosphate buffer (pH 7.5), 5 mg of keyholelimpet hemocyanin (KLH) (commercially available from Calbiochem) wasdissolved, and 1 mg of GMBS (N-γ-maleimidobutyryloxysuccinimide ester,commercially available from Dojindo Laboratories) was added to thesolution, followed by stirring the resulting mixture at room temperaturefor 1 hour. The reaction mixture was applied to PD-10 column(commercially available from Pharmacia) equilibrated with 0.1 Mphosphate buffer (pH 7.0) containing 1 mM of EDTA and eluted with thesame buffer. The initial 2.5 ml was discarded and the subsequent 2.0 mlwas collected.

[0059] To the resultant, about 1 mg of C4 synthesized in Example 1 in 1ml of water was added and the mixture was stirred at room temperaturefor 2 hours. The reaction mixture was transferred to a dialysis tube anddialyzed against phosphate buffer (PBS) overnight. The same procedurewas followed for C5 and C6 to obtain about 5 ml of solution ofKLH-peptide conjugate for each peptide. The measured amounts of proteinsfor C4-KLH, C5-KLH and C6-KLH were 768 μg/ml, 861 μg/ml and 1140 μg/ml,respectively.

Example 3 Preparation of Lipoproteins from Human Serum

[0060] On 4 ml of pooled human serum collected 2 hours after eating, 4ml of a solution prepared by dissolving 1.21 g of tris-hydroxymethylaminomethane, 9.0 g of sodium chloride and 0.372 g of disodium EDTA in 1liter of distilled water and then adjusting the pH to 7.4 (this solutionis hereinafter referred to as “d=1.006 solution”) was overlaid and theresultant was centrifuged at 26,000× g for 1 hour by Beckmanultracentrifuge. The upper layer was pooled as CM fraction. On the lowerlayer, the d=1.006 solution was overlaid and centrifuged at 114,000× gfor 20 hours. The upper layer was pooled as VLDL fraction. The densityof the lower layer was adjusted to 1.063 with sodium bromide solutionand the resultant was centrifuged at 114,000× g for 20 hours. Thesupernatant was pooled as LDL fraction. The pooled fractions wereconcentrated and used as the antigens for the antigen-antibodyreactions.

Example 4 Establishment of Hybridomas Producing

[0061] Anti-Apo-B-48 Monoclonal Antibody and Preparation ofAnti-Apo-B-48 Monoclonal Antibody

[0062] Hybridomas producing anti-apo-B-48 monoclonal antibodies wereestablished by immunizing BALB/C mice with C4-KLH, C5-KLH or C6-KLH andfusing spleen lymphocytes recovered from the immunized mice and myelomacells.

[0063] More particularly, C4-KLH, C5-KLH or C6-KLH were emulsified withFreund's complete adjuvant and the mice were immunized with theemulsions at a dose of 25 to 100 μg of the conjugate per mouse. Two tothree weeks later, each of the conjugates was emulsified with Freund'sincomplete adjuvant and the mice was additionally immunized with theemulsions at a dose of 25 to 100 μg of the conjugate per mouse. Serafrom the mice were sampled and checked for the existence ofanti-apo-B-48 antibody by Western blot (WB) method. The WB method wascarried out in the same manner as the WB method described below, whichwas carried out for the screening of the desired monoclonal antibody.The mouse immunized with C6-KLH exhibited the strongest band in the WBmethod. To this mouse, 25 to 100 μg of free C6-KLH was administeredintravenously. Three or four days after, spleen was removed from themouse and spleen cells were prepared therefrom.

[0064] Mouse myeloma cells (P3U1) preliminarily cultured on RPMI-1640medium and the obtained spleen cells were mixed at a ratio of 1:2 to1:5, and cell fusion was carried out using PEG (purchased fromBoehringer). The fused cells were suspended in HAT medium and thentransferred to wells of a 96-well culture plate, followed by culturingthe cells in a CO₂ incubator at 37° C.

[0065] The culture supernatants of the cells were screened by WB method.That is, the VLDL fraction prepared in Example 3 was subjected to 3-15%gradient SDS polyacrylamide gel electrophoresis (SDS-PAGE) and theelectrophoretic pattern was transferred to a nitrocellulose membrane toprepare a blotting membrane. The blotting membrane was blocked with skimmilk and then slit into the form of tapes. Each of the membranes in theform of a tape was inserted into each of the grooves of AccutranIncubation Tray (commercially available from S & S), and a mixture ofpooled culture media from 6 wells of the 96-well culture plate was addedto one of the grooves, followed by allowing reaction at room temperaturefor 1 hour under stirring.

[0066] The blotting membranes were washed three times with PBScontaining 0.05% Tween 20 (trademark) (this buffer is hereinafterreferred to as “washing buffer” ) for 5 minutes/wash under stirring, andperoxidase (POD)-labeled anti-mouse immunoglobulin antibody (purchasedfrom Daco) was added to each groove, followed by allowing reaction atroom temperature for 1 hour. The membranes were then washed with thewashing buffer 4 times in the same manner as described above, and thesubstrate 4-chloronaphthol was added. Thereafter, existence of the bandscorresponding to apo-B-48 was checked.

[0067] Using each of the culture media which constituted the mixture ofthe culture media from 6 wells added to the groove that expressed apositive band, WB was performed again as described above and the wellproducing the desired antibody was selected. The cells in the well werecloned by limiting dilution method. The cells producing theanti-apo-B-48 antibody were intraperitoneally administered to a mouse ina large amount, and ascites containing the anti-apo-B-48 monoclonalantibody was recovered-from the mouse. The monoclonal antibody waspurified from the ascites by using protein A-Sepharose (trademark).

[0068] This anti-apo-B-48 monoclonal antibody was named monoclonalantibody B48-151, and the hybridoma producing this monoclonal antibodyB48-151 was named hybridoma B48-151.

Example 5 Confirmation of Reaction Specificity of Monoclonal AntibodyB48-151

[0069] The reaction specificity of monoclonal antibody B48-151 wasexamined by WB method using CM, VLDL and LDL fractions.

[0070] More particularly, each of the above-mentioned fractions preparedin Example 3 as an antigen was subjected to 3-15% gradient SDS-PAGE andthe obtained electrophoretic pattern was transferred to a nitrocellulosemembrane. The obtained blotting membrane was blocked with skim milk andthe resulting membrane was subjected to reaction with the antibodies. Asthe antibodies, the monoclonal antibody B48-151, and as controls, ananti-apo-B-100 monoclonal antibody MAB014 (purchased from Chemicon) andan anti-apo-B goat serum (purchased from Chemicon) were used. Forfurther confirming the reaction specificity, inhibition test was carriedout using free C6. Some of the blotting membranes were subjected to CCBstaining to locate the positions of the proteins.

[0071] The antibody-antigen reactions were carried out as follows. Eachof the antibodies was dissolved in phosphate buffer containing 1% bovineserum albumin (1% BSA-PBS)(pH 7.4) to a concentration of 1 μg/ml and theresulting solution was allowed to react with each of the antigensblotted on the WB membrane at room temperature for 1 hour understirring. After washing the membrane three times for five minutes perwash with the washing buffer, POD-labeled anti-mouse immunoglobulinantibody (purchased from Daco) was added to the membrane and theresultant was allowed to react at room temperature for 1 hour. Afterwashing the membrane four times in the same manner as described above, asolution of the substrate 4-chloronaphthol was added, and the bands wereobserved. The results are shown in FIG. 1.

[0072] The inhibition test was carried out in the same manner asdescribed above except that C6 was present at a concentration of 5 μg/mlin the reaction between the WB membrane and each of the antibodies. Theresults are shown in FIG. 2.

[0073] As shown in FIG. 1, use of the monoclonal antibody B48-151exhibited a band only at the position corresponding to apo-B-48 having amolecular weight of a little more than 200,000, and a band correspondingto apo-B-100 having a molecular weight of about 550,000 was notobserved.

[0074] As shown in FIG. 2, the band corresponding to apo-B-48 exhibitedwhen the monoclonal antibody B48-151 was used disappeared under thecoexistence of C6.

[0075] These results clearly indicate that the monoclonal antibodyB48-151 specifically recognizes apo-B-48 but does not specificallyrecognize apo-B-100.

[0076] The band corresponding to apo-B-48 exhibited when VLDL fractionwas used was the thickest is presumably because CM remnant is containedin the VLDL fraction. That is, since the fractions showing differencesin particle size and weight were separated, the VLDL fractions may havebeen contaminated with chylomicron remnants to show immunoreactivityagainst apo-B-48.

Example 6 Measurement of Apo-B-48 by ELISA Using

[0077] Immobilized Monoclonal Antibody B48-151 Sandwich ELISA wasperformed using the apo-B-48 as an antigen extracted from the SDS-PAGEgel.

[0078] More particularly, by the same method as described in Example 2,SDS-PAGE was performed. The portion of the gel containing the apo-B-48band exhibited by using the VLDL fraction was cut out and the antigenwas eluted from the gel by Electroeluter (commercially available fromBio Rad). On the other hand, to each of the wells of an ELISA plate(Maxisorb commercially available from Nunc), 75 μl of the monoclonalantibody B48-151 in PBS (pH 7.4) at a concentration of 10 μg/ml wasadded and the plate was left to stand at 4° C. overnight, therebyadsorbing the antibody to the wells. To each well, 150 μp of 1% BSA-PBS(pH 7.4) was placed and the plate was incubated at 37° C. for 5 hours,thereby carrying out masking. After washing the plate three times withthe washing buffer, serially two-fold (2^(n)) diluted purified apo-B-48in 1% BSA-PBS from the concentration of 5 μg/ml was placed in each wellin an amount of 75 μl/well and the resultant was allowed to react at 37°C. for 1 hour.

[0079] After washing the plate three times with the washing buffer,POD-labeled anti-human apo-B antibody (purchased from Chemicon) wasplaced in an amount of 75 μl/well, and the resultant was allowed toreact at 37° C. for 1 hour.

[0080] The plate was then well washed with the washing buffer and thesubstrate ABTS was added to the wells in an amount of 75 μl/well and theresultant was left to stand at room temperature for 15 minutes, followedby measurement of absorbance at 405 nm.

[0081] To confirm reaction specificity, as a control, apo-B-100(purchased from Chemicon) was serially diluted in the same manner asdescribed above but from the concentration of 40 μg/ml, and used asantigens in the ELISA as described above.

[0082] The results are shown in FIG. 3. As shown in FIG. 3, apo-B-48 canbe measured by ELISA using immobilized monoclonal antibody B48-151 andapo-B-100 was not measured by this ELISA.

Example 7 Measurement of Apo-B-48 in Sera by ELISA Using ImmobilizedMonoclonal Antibody B48-151

[0083] Apo-B-48 was measured in the same manner as in Example 6 exceptthat the samples were sera 20-fold diluted with 1% BSA-PBS (pH 7.4). Thesample sera were pooled frozen sera from 8 healthy individuals (SampleNos. 1-8), collected when fasted or 1 hour after eating. The results areshown in FIG. 4.

[0084] As shown in FIG. 4, in all samples, the measured apo-B-48 valueswere higher at 1 hour after eating than those during fasting. This is inagreement with the behavior of CM.

Example 8 Treatment of Sera with Surfactants

[0085] The reaction in the ELISA using the immobilized monoclonalantibody B48-151 in case of adding various surfactants to the reactionmixture when the immobilized antibody and the sera were reacted wasstudied. The surfactants used were anionic surfactants which were SDS(purchased from Nacalai Tesque) and sodium deoxycholate (purchased fromWako Pure Chemicals), and nonionic surfactants which were Triton X-100(purchased from Nacalai Tesque), Triton X-114 (purchased from NacalaiTesque), Tween-20 (purchased from Nacalai Tesque), Tween-80 (purchasedfrom Nacalai Tesque), NP-40 (purchased from Sigma), MEGA-8 (purchasedfrom Dojindo Laboratories) and Brij-35 (purchased from Sigma).

[0086] Monoclonal antibody B48-151 dissolved in PBS (pH 7.4) at aconcentration of 10 μg/ml was placed in wells of an ELISA plate(Maxisorb, commercially available from Nunc) in an amount of 75 μl/well,and the plate was left to stand at 4° C. overnight, thereby adsorbingthe antibody to the wells. Then 1% BSA-PBS (pH 7.4) was added to thewells in an amount of 150 μl/well and the plate was incubated at 37° C.for 5 hours, thereby carrying out masking. After washing the plate threetimes with the washing buffer, sera 20-fold diluted with PBS (pH 7.4)containing one of the surfactants at a concentration of 2%, 0.4%, 0.08%or 0.016% by weight were placed to the wells in an amount of 75 μl/well,and reaction was allowed to occur at 37° C. for 1 hour. After washingthe plate three times with the washing buffer, anti-human apo-B-100monoclonal antibody (B100-228) labeled with alkaline phosphataseprepared by the method of Yoshitake et al. dissolved in PBS (pH 7.4) wasadded to the wells in an amount of 75 μl/well, and reaction was allowedto occur at 37° C. for 1 hour. The plate was then sufficiently washedwith the washing buffer and the substrate 4-nitrophenol phosphate wasadded to the wells in an amount of 75 μl/well. After incubating theplate at 37° C. for 30 minutes, absorbance at 405 nm was measured. Asthe samples, fresh sera from healthy individuals collected at 1 hourafter eating and fresh sera from healthy individuals collected whenfasted were used. The results are shown in FIG. 5. In FIG. 5, “Tx-100”indicates Triton X-100, “Tx-114” indicates Triton X-114, “Tw-20”indicates Tween 20, “Tw-80” indicates Tween 80, “Deoxy-ch.” indicatessodium deoxycholate, and PBS indicates PBS containing no surfactants.

[0087] As shown in FIG. 5, in cases where the serum was diluted with PBS(pH 7.4) which did not contain any surfactant, coloring was not observedat all, so that it was judged that the C-terminal epitope of apo-B-48was not exposed. In cases where the PBS (pH 7.4) containing a surfactantwas used, strong coloring was observed when a nonionic surfactant suchas Triton X-100, Tween 20 or NP-40 at a concentration of about 0.1% wasused. Thus, it was judged that the C-terminal epitope of apo-B-48 wasexposed by the treatments with these surfactants. On the other hand, incases where MEGA-8, Brij-35 or SDS was used, the coloring was week oralmost no coloring was observed. Taking the results of Example 9described below into consideration, it was judged that MEGA-8 has poorability to expose the C-terminal epitope of apo-B48; that SDS,especially at a concentration of not less than 0.1% inhibits theimmunological reaction; and that Brij-35 has a poor ability to exposethe C-terminal epitope of apo-B-48 and inhibits the immunologicalreaction.

Example 9 Influence by Surfactants on Immunological Reaction

[0088] The reaction between immobilized peptide C6 and the monoclonalantibody B48-151 when the same surfactants as in Example 8 were added tothe reaction mixture was studied. Peptide C6 dissolved in PBS (pH 7.4)at a concentration of 1 μg/ml was placed in wells of an ELISA plate(Maxisorb, commercially available from Nunc) in an amount of 75 μl/well,and the plate was left to stand at 4° C. overnight, thereby adsorbingthe peptide C6 to the wells. Then 1% BSA-PBS (pH 7.4) was added to thewells in an amount of 150 μl/well and the plate was incubated at 37° C.for 5 hours, thereby carrying out masking. After washing the plate threetimes with the washing buffer, monoclonal antibody B48-151 dissolved inPBS (pH 7.4) to a concentration of 2.5 μg/ml, which PBS contained one ofthe surfactants at a concentration of 2%, 0.4%, 0.08% or 0.016% byweight were placed to the wells in an amount of 75 μl/well, and reactionwas allowed to occur at 37° C. for 1 hour. After washing the plate threetimes with the washing buffer, POD-labeled mouse immunoglobulin antibody(purchased form Daco) was added to the wells in an amount of 75 μl/well,and reaction was allowed to occur at 37° C. for 1 hour. The plate wasthen sufficiently washed with the washing buffer and the substrate ABTSwas added to the wells in an amount of 75 μl/well. After incubating theplate at 37° C. for 15 minutes, absorbance at 405 nm was measured. Theresults are shown in FIG. 6.

[0089] As shown in FIG. 6, influence by a nonionic surfactant such asTriton X-100, Tween 20 or NP-40 on the immunological reaction was notobserved at all. On the other hand, influence by Brij-35 or SDS on theimmunological reaction was observed. Especially, SDS completelyinhibited the immunological reaction at a concentration of not less than0.1% by weight.

We claim:
 1. A monoclonal antibody which specifically binds to apo-B-48and which does not specifically bind to apo-B-100.
 2. The monoclonalantibody according to claim 1, of which corresponding epitope resides inC-terminal region of apo-B-48.
 3. The monoclonal antibody according toclaim 2, wherein said C-terminal region is 1st to 20th amino acids fromthe C-terminal of apo-B-48.
 4. The monoclonal antibody according toclaim 3, wherein said corresponding epitope contains the C-terminal ofapo-B-48.
 5. The monoclonal antibody according to claim 1, which isproduced by hybridoma B48-151 deposited with National Institute ofBioscience and Human-Technology, Agency of Industrial Science andTechnology under accession No. FERM BP-6473 or variants thereof.
 6. Themonoclonal antibody according to claim 5, which is produced by saidhybridoma B48-151.
 7. A hybridoma which produces said monoclonalantibody according to claim
 1. 8. The hybridoma according to claim 7,which is produced by immunizing a mammal with a peptide derived fromapo-B-48, recovering antibody-producing cells from said mammal, fusingthe antibody-producing cells with myeloma cells, and selecting ahybridoma which produces said monoclonal antibody according to claim 1.9. The hybridoma according to claim 8, wherein said peptide comprisesC-terminal region of apo-B-48.
 10. The hybridoma according to claim 9,wherein said peptide consists essentially of not less than 5 to not morethan 20 amino acids from the C-terminal of apo-B-48.
 11. The hybridomaaccording to claim 10, wherein said peptide is a conjugate of a peptideconsisting essentially of 1st-6th amino acids from the C-terminal ofapo-B-48 and a carrier protein.
 12. The hybridoma according to claim 8,wherein said peptide is conjugated with said carrier protein throughcystein residue attached to the N-terminal of said peptide.
 13. Thehybridoma according to claim 7, which is hybridoma B48-151 depositedwith National Institute of Bioscience and Human-Technology, Agency ofIndustrial Science and Technology under accession No. of FERM BP-6473 orvariants thereof.
 14. The hybridoma according to claim 13, which ishybridoma B48-151.
 15. A method for measuring apo-B-48 in a test sample,comprising utilizing antigen-antibody reaction between apo-B-48 in saidtest sample and said monoclonal antibody according to any one of claims1-6.
 16. The method according to claim 15, wherein said monoclonalantibody is immobilized on a solid carrier, and apo-B-48 immobilized onsaid carrier through said monoclonal antibody is measured after saidantigen-antibody reaction.
 17. The method according to claim 16, whichis carried out by ELISA.
 18. The method according to claim 15, whereinthe apo-B-48 in said test sample is subjected to a treatment by whichthe corresponding epitope of said monoclonal antibody is exposed beforeor simultaneously with said antigen-antibody reaction.
 19. The methodaccording to claim 18, wherein said treatment comprises treating saidsample with a surfactant.
 20. The method according to claim 19, whereinsaid surfactant is a nonionic surfactant.
 21. A reagent for immunoassayfor measuring apo-B-48 comprising said monoclonal antibody according toany one of claims 1-6.
 22. The reagent according to claim 21, whereinsaid monoclonal antibody is immobilized on a solid carrier.
 23. A kitfor immunoassay for measuring apo-B-48 comprising said monoclonalantibody according to any one of claims 1-6.
 24. The kit according toclaim 23, wherein said monoclonal antibody is immobilized on a solidcarrier.